.. /Understanding `const` vs `var` in Zig

2026-03-08T00:00:00.000Z

A practical explanation of the difference between const and var in Zig and when to use each.

Understanding const and var in Zig

When writing Zig programs, one of the first things you’ll notice is that variables must be declared using either const or var. Unlike many other languages where variables are mutable by default, Zig forces you to explicitly decide whether a value should be mutable.

This design encourages safer code and makes intent clearer.

In simple terms:

  • const is used for immutable values
  • var is used for mutable values

Understanding when to use each will make your Zig programs cleaner and easier to reason about.

Using const

A const declaration means the value cannot change after initialization.

This is the most common form of declaration in Zig, because many values in a program never actually change.

Example:

const std = @import("std");

pub fn main() void {
    const message = "Hello Zig!";
    const number = 42;

    std.debug.print("{s}\n", .{message});
    std.debug.print("{}\n", .{number});
}